1. Field of Invention
The present invention is directed to non-intrusive analysis and visual display of internal features of logs and, in particular, to systems and methods for scanning, detecting, and displaying internal features of a log, using computerized tomography.
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2. Related Art
The value of a board generally depends on the size of the board and number of defects in the board. Accordingly, sawmills, particularly when sawing valuable logs, attempt to maximize the yield of boards having large areas that are relatively free of defects. Naturally, a log with fewer defects provides better quality boards or lumber. Therefore, the commercial value of a log directly depends on the type and number of defects in the log.
Defects in a log commonly correspond to variations in a log""s composition or density. Such variations often arise from the natural growth process of the tree and correspond to knots, voids, or decay in the body of the tree. Some defects such as cracks or decay on the exterior of a log are clearly visible, but many internal defects or the extent thereof (e.g., interior decay and internal knots) are not fully visible to the naked eye. A buyer, typically, evaluates a log by considering the log""s shape, external indicators of internal defects, and knowledge of lumber grades. While experts such as log graders and sawyers are highly skilled in the evaluation of logs, they cannot possibly detect all internal defects of a log. Therefore, it is difficult to accurately distinguish a high quality log over a lower quality log that has a similar external appearance.
A person could more accurately estimate the value of a log if he could view and inspect the internal defects and undesirable features of the log. Accordingly, methods and systems that can efficiently detect and reveal the defects in the interior composition of a log with reasonable accuracy would be very helpful in evaluating a log""s worth.
One or more embodiments of the invention are directed to a system and method for non-intrusive analysis and visual display of the internal features of logs, using CT scanning technology. The system and method described herein may be also applicable to scanning objects other than a log. In one embodiment of the system, a log passes through a CT scanner in one continuous motion. The scanner includes an aperture to receive the log and one or more x-ray sources that revolve around the log, as it passes through the system, generating x-ray beams that traverse multiple cross-sections of the log.
An array of x-ray detectors detects attenuation of the x-ray beams that traverse the log. The attenuation of the x-ray beams is measured based on changes in the intensity of the x-ray beams as they pass through the log. These measurements are converted into scan data. The scan data contains information about multiple cross-sections of the log. A computer system reconstructs the scan data into two-dimensional or cross-sectional images of the log, by using a standard planar CT reconstruction technique.
The computer system also uses the scan data collected from multiple cross sections to construct three-dimensional images of the log. A three-dimensional image data set, in accordance with one aspect of the system, can thus be produced from data from two-dimensional images. In certain embodiments, interpolation, surface rendering, and ray tracing techniques may be used to produce three-dimensional image data sets, as well. In certain embodiments of the invention, three-dimensional image data sets are used to produce two-dimensional images with three-dimensional features using perspective and shading techniques.
According to one or more aspects of the invention, the system includes a retractable log driver (Push Dog) that drives the log on a transport bed through the scanner. In certain embodiments, the transport bed is preferably constructed of at least two parallel metal rails. The rails have a gap in the area where the x-rays pass through to avoid image distortion and interference with the scanning process. A loader or loading arm coupled to a mechanical actuator loads a log from a staying mechanism onto the transport bed. The loading arm, in a certain embodiment, includes one or more rails that form a portion of the transport bed when the loading arm is engaged in a loaded position. The loading arm can be activated in multiple positions to receive, load, or eject a log.
Embodiments of the system include an unloading arm for unloading logs from the transport bed onto a receiving mechanism. The receiving mechanism transitions the logs to a storage area, for example. The staying and receiving mechanisms can be represented by a variety of devices (e.g., xe2x80x9ctransportxe2x80x9d, xe2x80x9clog haulxe2x80x9d, xe2x80x9chourglass rollersxe2x80x9d, xe2x80x9clog kicker, etc.). The unloading arm may also include one or more rails that form a portion of the transport bed.
Before the log driver engages the log, a sensor mechanism determines whether a log loaded on the system can go through the aperture of the CT scanner. If the sensor detects an oversized log, the log is ejected from the transport bed. In certain embodiments, the log is ejected when the loading arm moves to an eject position. If the sensor determines that the log can safely clear the aperture of the scanner, then the log driver engages at least one end of the log and drives the log through the scanner. The driver is configured to displace the log at a speed that allows the scanning system to capture sufficient data from multiple cross-sections of the log for display and analysis purposes.
A processing system converts captured data, also referred to as scan data, into two or three-dimensional density distribution images that display the defects within the body of the log so that the defects are recognizable by a human operator or a computing system. In one or more embodiments, an end unit (e.g., hold back dog) engages the log at the end opposite to the point of engagement of the log driver to add stability to the positioning and movement of the log on the transport bed. Once the complete length of the log has been driven through the scanner, the log driver is retracted to its original position so that another log can be loaded. The end unit can further include marking systems that mark the log for sawing or identification.
Other embodiments of the invention may include a revolving belt mechanism with multiple log drivers installed at successive intervals around the belt so that a second log driver is in position to engage a second log when the scanning process for the first log is complete. This avoids the requirement for having a retracting mechanism. In either implementation, the loading arm is configured in such a way to allow for loading a second log immediately after the first log has gone through the scanning process.
The scan data and the images produced as the result of CT scanning and reconstruction are useful to a log purchaser or sawyer to evaluate the worth and usefulness of the log for producing certain quality boards. For example, the system can reconstruct scan data to simulate a longitudinal cut through the log producing the image of a virtual board. The system can also reconstruct other images such as three-dimensional views of the log that display the interior defective regions of the log, the type of defect (e.g., decay, cracks, knots, etc.), and the exact location of each undesirable feature.
Certain images, according to an embodiment of the invention, are produced so that the exterior surface of the log appears transparent and defects appear opaque and/or color-coded so that the defects are easily identified. In accordance with one aspect of the invention, the system may determine an optimal cutting solution for the log based on information provided about the log""s intended use, the type of each defect, and respective distance between the defects. Other embodiments may provide a purchaser with a log""s grade, estimated value, or most suitable or profitable cutting solution.
In accordance with another aspect of the invention, a log is marked with a reference mark that indicates the orientation of the log during the scanning process. This information can be used during sawing or image processing to accurately identify the location of the defective or undesirable regions in the log. Using a reference mark, a sawyer or a computerized sawing machine can appropriately position the log""s orientation for a specific cut. The reference mark can be simple stripes or markings painted on one or both ends of the log. The markings can include more sophisticated coding such as bar codes or magnetic strips that contain additional information about the log (e.g., grade, sample cross-sectional views, sawing solutions, etc.). The reference marks can be placed on the logs by a marking mechanism. In one embodiment of the system, the marking mechanism is integrated into the log driver, end unit, or both.